The present invention relates to polymer compositions having excellent resilience which are particularly suitable as golf ball-forming materials, and to golf balls made using such polymer compositions.
Efforts to confer golf balls with an excellent rebound have until now focused on and optimized one or more indicator of the polybutadiene used as the base rubber, such as the Mooney viscosity, polymerization catalyst, solvent viscosity and molecular weight distribution. See, for example, Patent Document 1: JP-A 2004-292667; Patent Document 2: U.S. Pat. No. 6,818,705; Patent Document 3: JP-A 2002-355336; Patent Document 4: JP-A 2002-355337; Patent Document 5: JP-A 2002-355338; Patent Document 6: JP-A 2002-355339; Patent Document 7: JP-A 2002-355340; and Patent Document 8: JP-A 2002-356581.
For example, Patent Document 1 (JP-A 2004-292667) describes, as a base rubber for golf balls, a polybutadiene having a Mooney viscosity of from 30 to 42 and a molecular weight distribution (Mw/Mn) of from 2.5 to 3.8. Patent Document 2 (U.S. Pat. No. 6,818,705) describes, for the same purpose, a polybutadiene having a molecular weight of at least 200,000 and a resilience index of at least 40.
However, because many golfers desire golf balls capable of traveling a longer distance, there exists a need for the development of golf balls having an even better rebound.
Patent Document 9 (JP-B 39-6810) and Patent Document 10 (JP-B 53-41173) describe basic methods for preparing ionomers, although these methods have a number of associated problems, such as an unpleasant odor during neutralization and poor dispersion of white particles. The physical properties of the ionomers were subsequently improved, resulting in the disclosure of improved ionomers, such as those described in Patent Document 11 (JP-A 2002-514112), Patent Document 12 (JP-A 2003-512495) and Patent Document 13 (JP-A 2002-527597). However, from the standpoint of the ball rebound, even further improvements in the physical properties of the ionomer are desired.
Patent Document 1: JP-A 2004-292667
Patent Document 2: U.S. Pat. No. 6,818,705
Patent Document 3: JP-A 2002-355336
Patent Document 4: JP-A 2002-355337
Patent Document 5: JP-A 2002-355338
Patent Document 6: JP-A 2002-355339
Patent Document 7: JP-A 2002-355340
Patent Document 8: JP-A 2002-356581
Patent Document 9: JP-B 39-6810
Patent Document 10: JP-B 53-41173
Patent Document 11: JP-A 2002-514112
Patent Document 12: JP-A 2003-512495
Patent Document 13: JP-A 2002-527597